One method to control intake and exhaust valve operation during engine operation is described in U.S. Pat. No. 6,374,813. This method presents a means to control electromagnetically actuated valves to promote cylinder air charge swirl. Valves are operated independently and control is based on operating conditions of the engine. Further, the disclosure also describes several valve configurations that may be operated in one or more operational modes.
The inventors herein have determined that the above-mentioned method can have several disadvantages. Specifically, the above approach requires all valves to be electrically actuated, and thus may unnecessarily increase cost.
Also, the above-mentioned approach may increase emissions where an exhaust system design is asymmetric, e.g., where catalyst locations are different between cylinder banks of an engine. Typically, in asymmetric designs, time to efficient operation after a start varies between the asymmetric exhaust branches. For example, six cylinder engines are often mounted in a transverse configuration that may not permit construction of symmetric cylinder bank exhaust after treatment systems. And since prior approaches treat all cylinders similarly, this symmetric operation of prior approaches can result in increased emissions.